Method and device for transmitting ACK/NACK in wireless communication system

ABSTRACT

Provided are a method and a device for transmitting an acknowledgement/not-acknowledgement (ACK/NACK) of a terminal which is set with a plurality of serving cells. The method comprises the steps of: receiving data in a subframe n of a second serving cell; and transmitting an ACK/NACK signal for the data in a subframe n+k SCC (n) of a first serving cell connected to the subframe n of the second serving cell, wherein the first serving cell is a primary cell for the terminal to execute an initial connection establishment procedure or a connection reestablishment procedure, and uses a frequency division duplex (FDD) wireless frame, the second serving cell is a secondary cell allocated to the terminal in addition to the primary cell, and uses a time division duplex (TDD) wireless frame, and the k SCC (n) is a previously determined value.

This Application is a 35 U.S.C. §371 National Stage Entry ofInternational Application No. PCT/KR2012/001841, filed Mar. 14, 2012 andclaims the benefit of U.S. Provisional Application Nos. 61/452,164,filed Mar. 14, 2011 and 61/467,387, filed Mar. 25, 2011, all of whichare incorporated by reference in their entirety herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wireless communication and, moreparticularly, to a method and apparatus for transmitting receptionacknowledgement for a Hybrid Automatic Repeat reQuest (HARQ) in awireless communication system in which serving cells using differenttypes of radio frames are aggregated.

2. Related Art

Long Term Evolution (LTE) based on 3^(rd) Generation Partnership Project(3GPP) Technical Specification (TS) Release 8 is the leadingnext-generation mobile communication standard.

As disclosed in 3GPP TS 36.211 V8.7.0 (2009 May) “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, in LTE, a physical channel can be divided into a PhysicalDownlink Shared Channel (PDSCH) and a Physical Downlink Control Channel(PDCCH), that is, downlink channels, and a Physical Uplink SharedChannel (PUSCH) and a Physical Uplink Control Channel (PUSCH), that is,uplink channels.

A PUCCH is an uplink control channel used to send uplink controlinformation, such as a Hybrid Automatic Repeat reQuest (HARQ), anacknowledgement/not-acknowledgement (ACK/NACK) signal, a Channel QualityIndicator (CQI), and a Scheduling Request (SR).

Meanwhile, 3GPP LTE-Advanced (A) that is the evolution of 3GPP LTE is inprogress. Technology introduced into 3GPP LTE-A includes a carrieraggregation.

A carrier aggregation uses a plurality of component carriers. Acomponent carrier is defined by the center frequency and a bandwidth.One downlink component carrier or a pair of an uplink component carrierand a downlink component carrier correspond to one cell. It can be saidthat a terminal being served using a plurality of downlink componentcarriers is being served from a plurality of serving cells.

In a Time Division Duplex (TDD) system, the same frequency is used inuplink and downlink. Accordingly, one or more DL subframes areassociated with an UL subframe. The “association” means thattransmission/reception in the DL subframe is associated withtransmission/reception in the UL subframe. For example, when a transportblock is received in a plurality of DL subframes, a terminal sends HARQACK/NACK (hereinafter referred to as ACK/NACK) for the transport blockin an UL subframe associated with a plurality of DL subframes. Here, aminimum time is necessary to send the ACK/NACK. This is because the timetaken to process the transport block and the time taken to process theACK/NACK are necessary.

In a Frequency Division Duplex (FDD) system, different frequencies areused in uplink and downlink. An UL subframe and a DL subframe have a 1:1relationship. In this case, ACK/NACK for a transport block received in aDL subframe is transmitted in an UL subframe after four subframes.

Meanwhile, in the next-generation wireless communication system, aserving cell using TDD and a serving cell using FDD can be aggregated.That is, a plurality of serving cells using different types of radioframes can be allocated to a terminal. In this case, whether ACK/NACKwill be transmitted using what method is problematic.

SUMMARY OF THE INVENTION

An object of the present invention is to provide method and apparatusfor transmitting ACK/NACK in a wireless communication system in which aplurality of serving cells using different types of radio frames isaggregated.

In one aspect, there is provided an acknowledgement/not-acknowledgement(ACK/NACK) transmission method of UE in which a plurality of servingcells has been configured. The method includes the steps of receivingdata in a subframe n of a second serving cell and sending an ACK/NACKsignal for the data in a subframe n+k_(SCC)(n) of a first serving cellwhich is associated with the subframe n of the second serving cell,wherein the first serving cell is a primary cell in which the UEperforms an initial connection establishment procedure or connectionre-establishment procedure with a base station, the first serving celluses a Frequency Division Duplex (FDD) radio frame, the second servingcell is a secondary cell additionally allocated to the UE in addition tothe primary cell, the second serving cell uses a Time Division Duplex(TDD) radio frame, and the k_(SCC)(n) is a predetermined value.

The k_(SCC)(n) is a value identical with ACK/NACK timing in the firstserving cell and may be four subframes.

The method further includes the steps of receiving data in a subframe nof the first serving cell and sending an ACK/NACK signal in the subframen+k_(SCC)(n) of the first serving cell which is associated with thesubframe n of the first serving cell. The subframe n+k_(SCC)(n) may bean uplink subframe spaced apart from the subframe n of the first servingcell by four subframes.

The method further includes the steps of receiving a first downlinkgrant for the data, received in the subframe n of the first servingcell, in the first serving cell and receiving a second downlink grantfor the data received in the subframe n of the second serving cell, inthe first serving cell. The number of bits of the first downlink grantmay be the same as that of the second downlink grant.

The method further includes the step of receiving uplink (UL)-downlink(DL) configuration information about the TDD radio frame used in thesecond serving cell through the first serving cell.

The method further includes the steps of receiving data in a subframe nof a third serving cell and sending an ACK/NACK signal for data,received in the third serving cell, in the subframe k_(SCC)(n) of thefirst serving cell which is associated with the subframe n of the thirdserving cell. The third serving cell is a secondary cell additionallyallocated to the UE in addition to the primary cell, and the thirdserving cell may use a TDD radio frame.

In another aspect, there is provided an ACK/NACK transmission method ofUE in which a plurality of serving cells has been configured. The methodincludes the steps of receiving data in a subframe n−k of a secondserving cell and sending an ACK/NACK signal for the data in a subframe nof a first serving cell which is associated with the subframe n−k of thesecond serving cell, wherein the first serving cell is a primary cell inwhich the UE performs an initial connection establishment procedure orconnection re-establishment procedure with a base station, the firstserving cell uses a Frequency Division Duplex (FDD) radio frame, thesecond serving cell is a secondary cell additionally allocated to the UEin addition to the primary cell, the second serving cell uses a TimeDivision Duplex (TDD) radio frame, and in the subframe n−k, the k isdetermined to be a value identical with ACK/NACK timing of the secondserving cell.

The method may further include the step of receiving UL-DL configurationinformation about the TDD radio frame used in the second serving cellthrough the first serving cell.

The method may further include the steps of receiving data in a subframen−k of a third serving cell and sending an ACK/NACK signal for the datain the subframe n of the first serving cell which is associated with thesubframe n−k of the third serving cell. The third serving cell is asecondary cell additionally allocated to the UE in addition to theprimary cell, and the third serving cell may use a TDD radio frame.

In yet another aspect, there is provided UE. The UE include a RadioFrequency (RF) unit sending and receiving radio signals and a processorconnected to the RF unit, wherein the processor receives data in asubframe n of a second serving cell and sends an ACK/NACK signal for thedata in a subframe n+k_(SCC)(n) of a first serving cell which isassociated with the subframe n of the second serving cell, the firstserving cell is a primary cell in which the UE performs an initialconnection establishment procedure or connection re-establishmentprocedure with a base station, the first serving cell uses a FrequencyDivision Duplex (FDD) radio frame, the second serving cell is asecondary cell additionally allocated in addition to the primary cell,the second serving cell uses a Time Division Duplex (TDD) radio frame,and the k_(SCC)(n) is a predetermined value.

ACK/NACK transmission timing for a terminal that operates in a wirelesscommunication system in which a plurality of serving cells usingdifferent types of radio frames is aggregated is guaranteed inaccordance with the present invention. Accordingly, system performanceis improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of an FDD radio frame.

FIG. 2 shows the structure of a TDD radio frame.

FIG. 3 shows an example of a resource grid for one downlink slot.

FIG. 4 shows the structure of a DL subframe.

FIG. 5 shows the structure of an UL subframe.

FIG. 6 shows the channel structure of a PUCCH format 1b in a normal CP.

FIG. 7 shows the channel structure of PUCCH formats 2/2a/2b in a normalCP.

FIG. 8 illustrates an Enhanced (E)-PUCCH format based on blockspreading.

FIG. 9 shows an example of a comparison between a single carrier systemand a carrier aggregation system.

FIG. 10 shows one example in which a plurality of serving cells usesdifferent types of radio frames in a wireless communication system.

FIG. 11 shows a method of transmitting ACK/NACK for downlink datareceived through a primary cell.

FIG. 12 shows a method of transmitting ACK/NACK for downlink datareceived through a secondary cell.

FIG. 13 shows Method 1 when ‘k_(min)’ is four subframes.

FIG. 14 shows Method 2.

FIG. 15 is a block diagram showing a wireless device in which anembodiment of the present invention is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

User Equipment (UE) can be fixed or can have mobility. UE can also becalled another term, such as a Mobile Station (MS), a Mobile Terminal(MT), a User Terminal (UT), a Subscriber Station (SS), a wirelessdevice, a Personal Digital Assistant (PDA), a wireless modem, or ahandheld device.

The BS commonly refers to a fixed station that communicates with UE. TheBS can also be called another tem, such as an evolved-NodeB (eNodeB), aBase Transceiver System (BTS), or an access point.

Communication from a BS to UE is called downlink (DL), and communicationfrom UE to a BS is called uplink (UL). A wireless communication systemincluding a BS and UE can be a Time Division Duplex (TDD) system or aFrequency Division Duplex (FDD) system. A TDD system is a wirelesscommunication system that performs UL and DL transmission/receptionusing different times in the same frequency band. An FDD system is awireless communication system that enables UL and DLtransmission/reception at the same time using different frequency bands.A wireless communication system can perform communication using radioframes.

FIG. 1 shows the structure of an FDD radio frame.

The FDD radio frame includes 10 subframes, and one subframe includes twoconsecutive slots. The slots within the radio frame are assigned indices0˜19. The time that is taken for one subframe to be transmitted iscalled a Transmission Time Interval (TTI). A TTI can be a minimumscheduling unit. For example, the length of one subframe can be 1 ms,and the length of one slot can be 0.5 ms.

FIG. 2 shows the structure of a TDD radio frame.

Referring to FIG. 2, subframes having an index #1 and an index #6 arecalled special subframes, and the subframe includes a Downlink PilotTime Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot Time Slot(UpPTS). The DwPTS is used in initial cell search, synchronization, orchannel estimation in UE. The UpPTS is used for channel estimation in aBS and for the uplink transmission synchronization of UE. The GP is aninterval in which interference occurring in UL due to the multi-pathdelay of a DL signal between UL and DL is removed.

In TDD, a downlink (DL) subframe and an uplink (UL) subframe coexist inone radio frame. Table 1 shows an example of the UL-DL configuration ofa radio frame.

TABLE 1 UL-DL DL-to-UL config- switch-point Subframe n urationperiodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S UU D D S U U U 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 410 ms D S U U D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U DS U U D

In Table 1, ‘D’ indicates a DL subframe, ‘U’ indicates an UL subframe,and ‘S’ indicates a special subframe. When an UL-DL configuration isreceived from a BS, UE can be aware whether each subframe in a radioframe is a DL subframe or an UL subframe. Hereinafter, reference can bemade to Table 1 for an UL-DL configuration N (N is any one of 0 to 6).

FIG. 3 shows an example of a resource grid for one downlink slot.

Referring to FIG. 3, the downlink slot includes a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbol in the timedomain and includes N_(RB) Resource Blocks (RBs) in the frequencydomain. The RBs includes one slot in the time domain and a plurality ofconsecutive subcarrier in the frequency domain in a resource allocationunit. The number of RBs N_(RB) included in the downlink slot depends ona downlink transmission bandwidth N^(DL) configured in a cell. Forexample, in an LTE system, the N_(RB) can be any one of 6 to 110. Anuplink slot can have the same structure as the downlink slot.

Each element on the resource grid is called a Resource Element (RE). TheRE on the resource grid can be identified by an index pair (k,l) withina slot. Here, k (k=0, . . . , N_(RB)×12−1) is a subcarrier index withinthe frequency domain, and l (l=0, . . . , 6) is an OFDM symbol indexwithin the time domain.

Although 7×12 REs including 7 OFDM symbols in the time domain and 12subcarrier in the frequency domain have been illustrated as beingincluded in one RB in FIG. 3, the number of OFDM symbols and the numberof subcarriers within an RB are not limited thereto. The number of OFDMsymbols and the number of subcarriers can be changed in various waysdepending on the length of a CP, frequency spacing, etc. In one OFDMsymbol, one of 128, 256, 512, 1024, 1536, and 2048 can be selected andused as the number of subcarriers.

FIG. 4 shows the structure of a DL subframe.

Referring to FIG. 4, a downlink (DL) subframe is divided into a controlregion and a data region in the time domain. The control region includesa maximum of former 3 (maximum 4 according to circumstances) OFDMsymbols of a first slot within a subframe, but the number of OFDMsymbols included in the control region can be changed. A control channeldifferent from a physical downlink control channel (PDCCH) is allocatedto the control region, and a physical downlink shared channel (PDSCH) isallocated to the data region.

As disclosed in 3GPP TS 36.211 V8.7.0, in 3GPP LTE, physical channelscan be divided into a physical downlink shared channel (PDSCH) and aphysical uplink shared channel (PUSCH), that is, data channels, and aphysical downlink control channel (PDCCH), a physical control formatindicator channel (PCFICH), a physical hybrid-ARQ indicator channel(PHICH), and a physical uplink control channel (PUSCH), that is, controlchannels.

A PCFICH that is transmitted in the first OFDM symbol of a subframecarries a Control Format Indicator (CFI) regarding the number of OFDMsymbols (i.e., the size of a control region) that are used to sendcontrol channels within the subframe. UE first receives a CFI on aPCFICH and then monitors PDCCHs. Unlike in a PDCCH, a PCFICH is notsubject to blind decoding, but is transmitted through the fixed PCFICHresources of a subframe.

A PHICH carries a positive-acknowledgement(ACK)/negative-acknowledgement (NACK) signal for an uplink HybridAutomatic Repeat reQuest (HARM). An ACK/NACK signal for uplink (UL) dataon a PUSCH which is transmitted by UE is transmitted on a PHICH.

A physical broadcast channel (PBCH) is transmitted in the former 4 OFDMsymbols of a second slot within the first subframe of a radio frame. ThePBCH carries system information that is essential for UE to communicatewith a BS, and system information transmitted through a PBCH is called aMaster Information Block (MIB). In contrast, system informationtransmitted on a PDSCH indicated by a PDCCH is called a SystemInformation Block (SIB).

Control information transmitted through a PDCCH is called DownlinkControl Information (DCI). DCI can include the resource allocation of aPDSCH (this is also called a DL grant), the resource allocation of aPUSCH (this is also called an UL grant), a set of transmit power controlcommands for individual MSs within a specific UE group and/or theactivation of a Voice over Internet Protocol (VoIP).

FIG. 5 shows the structure of an UL subframe.

Referring to FIG. 5, the UL subframe can be divided into a controlregion to which a physical uplink control channel (PUSCH) for carryinguplink control information is allocated and a data region to which aphysical uplink shared channel (PUSCH) for carrying user data isallocated in the frequency domain.

A PUCCH is allocated with an RB pair in a subframe. RBs that belong toan RB pair occupy different subcarriers in a first slot and a secondslot. An RB pair has the same RB index m.

In accordance with 3GPP TS 36.211 V8.7.0, a PUCCH supports multipleformats. A PUCCH having a different number of bits in each subframe canbe used according to a modulation scheme that is dependent on a PUCCHformat.

Table 2 below shows an example of modulation schemes and the number ofbits per subframe according to PUCCH formats.

TABLE 2 PUCCH format Modulation scheme Number of bits per subframe 1 N/AN/A 1a BPSK 1 1b QPSK 2 2 QPSK 20 2a QPSK + BPSK 21 2b QPSK + QPSK 22

The PUCCH format 1 is used to send a Scheduling Request (SR), the PUCCHformats 1a/1b are used to send an ACK/NACK signal for an HARQ, the PUCCHformat 2 is used to send a CQI, and the PUCCH formats 2a/2b are used tosend a CQI and an ACK/NACK signal at the same time. When only anACK/NACK signal is transmitted in a subframe, the PUCCH formats 1a/1bare used. When only an SR is transmitted, the PUCCH format 1 is used.When an SR and an ACK/NACK signal are transmitted at the same time, thePUCCH format 1 is used. The ACK/NACK signal is modulated into resourcesallocated to the SR and is then transmitted.

All the PUCCH formats use the Cyclic Shift (CS) of a sequence in eachOFDM symbol. A CS sequence is generated by cyclically shifting a basesequence by a specific CS amount. The specific CS amount is indicated bya CS index.

An example in which a base sequence r_(u)(n) has been defined is thesame as the following equation.r _(u)(n)−e ^(jb(n)π/4)  [Equation 1]

Here, u is a root index, n is an element index wherein 0≦n≦N−1, and N isthe length of the base sequence. b(n) is defined in section 5.5 of 3GPPTS 36.211 V8.7.0.

The length of a sequence is the same as the number of elements includedin the sequence. U can be determined by a cell identifier (ID), a slotnumber within a radio frame, etc. Assuming that a base sequence ismapped to one resource block in the frequency domain, the length N ofthe base sequence becomes 12 because one resource block includes 12subcarriers. A different base sequence is defined depending on adifferent root index.

A CS sequence r(n, I_(cs)) can be generated by cyclically shifting thebase sequence r(n) as in Equation 2.

$\begin{matrix}{{{r( {n,I_{cs}} )} = {{r(n)} \cdot {\exp( \frac{{j2\pi}\; I_{cs}n}{N} )}}},{0 \leq I_{cs} \leq {N - 1}}} & \lbrack {{Equation}\mspace{14mu} 2} \rbrack\end{matrix}$

Here, I_(cs) is a CS index indicative of a CS amount (0≦I_(cs)≦N−1).

An available CS index of a base sequence refers to a CS index that canbe derived from the base sequence according to a CS interval. Forexample, the length of a base sequence is 12 and a CS interval is 1, atotal number of available CS indices of the base sequence becomes 12.Or, if the length of a base sequence is 12 and a CS interval is 2, atotal number of available CS indices of the base sequence becomes 6.

FIG. 6 shows the channel structure of the PUCCH format 1b in a normalCP.

One slot includes 7 OFDM symbols, the 3 OFDM symbols become ReferenceSignal (RS) OFDM symbols for a reference signal, and the 4 OFDM symbolsbecome data OFDM symbols for an ACK/NACK signal.

In the PUCCH format 1b, a modulation symbol d(0) is generated byperforming Quadrature Phase Shift Keying (QPSK) modulation on an encoded2-bit ACK/NACK signal.

A CS index I_(cs) can vary depending on a slot number ‘ns’ within aradio frame and/or a symbol index ‘1’ within a slot.

In a normal CP, 4 data OFDM symbols for sending an ACK/NACK signal arepresent in one slot. It is assumed that corresponding CS indices inrespective data OFDM symbols are I_(cs0), I_(cs1), I_(cs2), and I_(cs3).

The modulation symbol d(0) is spread into a CS sequence r(n,Ics).Assuming that a 1-dimensional spread sequence corresponding to an(i+1)^(th) OFDM symbol is m(i) in a slot,

-   -   {m(0), m(1), m(2), m(3)}={d(0)r(n,I_(cs0)), d(0)r(n,I_(cs1)),        d(0)r(n,I_(cs2)), d(0)r(n,I_(cs3))} can be obtained.

In order to increase a UE capacity, the 1-dimensional spread sequencecan be spread using an orthogonal sequence. The following sequence isused as an orthogonal sequence w_(i)(k) (i is a sequence index, 0≦k≦K−1)wherein a spreading factor K=4.

TABLE 3 Index (i) [w_(i)(0), w_(i)(1), w_(i)(2), w_(i)(3)] 0 [+1, +1,+1, +1] 1 [+1, −1, +1, −1] 2 [+1, −1, −1, +1]

The following sequence is used as an orthogonal sequence w_(i)(k) (i isa sequence index, 0≦k≦K−1) wherein a spreading factor K=3.

TABLE 4 Index (i) [w_(i)(0), w_(i)(1), w_(i)(2)] 0 [+1, +1, +1] 1 [+1,e^(j2π/3), e^(j4π/3)] 2 [+1, e^(j4π/3), e^(j2π/3)]

A different spreading factor can be used in each slot.

Accordingly, assuming that a specific orthogonal sequence index i isgiven, 2-dimensional spread sequences {s(0), s(1), s(2), s(3)} can beexpressed as follows.

-   -   {s(0), s(1), s(2), s(3)}={w_(i)(0)m(0), w_(i)(1)m(1),        w_(i)(2)m(2), w_(i)(3)m(3)}

The 2-dimensional spread sequences {s(0), s(1), s(2), s(3)} are subjectto IFFT and then transmitted in a corresponding OFDM symbol.Accordingly, an ACK/NACK signal is transmitted on a PUCCH.

A reference signal having the PUCCH format 1b is also transmitted byspreading the reference signal into an orthogonal sequence aftercyclically shifting a base sequence r(n). Assuming that CS indicescorresponding to 3 RS OFDM symbols are I_(cs4), I_(cs5), and I_(cs6), 3CS sequences r(n,I_(cs4)), r(n,I_(cs5)), r(n,I_(cs6)) can be obtained.The 3 CS sequences are spread into an orthogonal sequence w^(RS) _(i)(k)wherein K=3.

An orthogonal sequence index i, a CS index I_(cs), and an RB index m areparameters necessary to configure a PUCCH and are also resources used toclassify PUCCHs (or MSs). If the number of available CSs is 12 and thenumber of available orthogonal sequence indices is 3, a PUCCH for atotal of 36 MSs can be multiplexed with one RB.

In 3GPP LTE, a resource index n⁽¹⁾ _(PUCCH) is defined so that UE canobtain the three parameters for configuring a PUCCH. The resource indexn⁽¹⁾ _(PUCCH)=n_(CCE)+N⁽¹⁾ _(PUCCH), wherein n_(CCE) is the number ofthe first CCE used to send a corresponding PDCCH (i.e., PDCCH includingthe allocation of DL resources used to received downlink datacorresponding to an ACK/NACK signal), and N⁽¹⁾ _(PUCCH) is a parameterthat is informed of UE by a BS through a higher layer message.

Time, frequency, and code resources used to send an ACK/NACK signal arecalled ACK/NACK resources or PUCCH resources. As described above, anindex of ACK/NACK resources (called an ACK/NACK resource index or PUCCHindex) used to send an ACK/NACK signal on a PUCCH can be represented asat least one of an orthogonal sequence index i, a CS index I_(cs), an RBindex m, and an index for calculating the 3 indices. ACK/NACK resourcescan include at least one of an orthogonal sequence, a CS, a resourceblock, and a combination of them.

FIG. 7 shows the channel structure of the PUCCH formats 2/2a/2b in anormal CP.

Referring to FIG. 7, in a normal CP, OFDM symbols 1 and 5 (i.e., secondand sixth OFDM symbols) are used to send a demodulation reference signal(DM RS), that is, an uplink reference signal, and the remaining OFDMsymbols are used to send a CQI. In the case of an extended CP, an OFDMsymbol 3 (fourth symbol) is used for a DM RS.

10 CQI information bits can be subject to channel coding at a 1/2 coderate, for example, thus becoming 20 coded bits. Reed-Muller code can beused in the channel coding. Next, the 20 coded bits are scramble andthen subject to QPSK constellation mapping, thereby generating a QPSKmodulation symbol (d(0) to d(4) in a slot 0). Each QPSK modulationsymbol is modulated in a cyclic shift of a base RS sequence ‘r(n)’having a length of 12, subject to IFFT, and then transmitted in each of10 SC-FDMA symbols within a subframe. Uniformly spaced 12 CSs enable 12different MSs to be orthogonally multiplexed in the same PUCCH RB. Abase RS sequence ‘r(n)’ having a length of 12 can be used as a DM RSsequence applied to OFDM symbols 1 and 5.

FIG. 8 illustrates an Enhanced (E)-PUCCH format based on blockspreading.

An E-PUCCH format is also called the PUCCH format 3.

Referring to FIG. 8, the E-PUCCH format is a PUCCH format that uses ablock spreading scheme. The block spreading scheme means a method ofmultiplexing a modulation symbol sequence that has been modulated frommulti-bit ACK/NACK using block spreading code. An SC-FDMA scheme can beused in the block spreading scheme. Here, the SC-FDMA scheme means atransmission method of performing IFFT after DFT spreading.

An E-PUCCH format is transmitted in such a manner that a symbol sequence(e.g., ACK/NACK symbol sequence) is spread in the time domain by way ofblock spreading code. Orthogonal Cover Code (OCC) can be used as theblock spreading code. The control signals of several MSs can bemultiplexed by the block spreading code. In the PUCCH format 2, onesymbol sequence is transmitted in the time domain, and UE multiplexingis performed using the cyclic shift of a Constant Amplitude ZeroAuto-Correlation (CAZAC) sequence. In contrast, in the E-PUCCH format, asymbol sequence including one or more symbols is transmitted in thefrequency domain of each data symbol, the symbol sequence is spread inthe time domain by way of block spreading code, and UE multiplexing isperformed. An example in which 2 RS symbols are used in one slot hasbeen illustrated in FIG. 8, but the present invention is not limitedthereto. 3 RS symbols can be used, and OCC in which a spreading factorvalue is 4 may be used. An RS symbol can be generated from a CAZACsequence having a specific CS and can be transmitted in such a mannerthat a plurality of RS symbols in the time domain has been multiplied bya specific OCC.

A carrier aggregation system is described below. The carrier aggregationsystem is also called a multiple carrier system.

A 3GPP LTE system supports a case where a DL bandwidth and an ULbandwidth are differently configured, but one Component Carrier (CC) isa precondition in this case. A 3GPP LTE system supports a maximum of 20MHz and can be different in an UL bandwidth and a DL bandwidth, butsupports only one CC in each of UL and DL.

A CA (also called a bandwidth aggregation or a spectrum aggregation)supports a plurality of CCs. For example, if 5 CCs are allocated as thegranularity of a carrier unit having a 20 MHz bandwidth, a maximum of a100 MHz bandwidth can be supported.

One DL CC or a pair of an UL CC and a DL CC can correspond to one cell.Accordingly, UE that communicates with a BS through a plurality of DLCCs can be said to be served from a plurality of serving cells.

FIG. 9 shows an example of a comparison between a single carrier systemand a carrier aggregation system.

A carrier aggregation system (FIG. 9 (b)) has been illustrated asincluding three DL CCs and three UL CCs, but the number of DL CCs and ULCCs is not limited. A PDCCH and a PDSCH can be independently transmittedin each DL CC, and a PUCCH and a PUSCH can be independently transmittedin each UL CC. Or, a PUCCH may be transmitted only through a specific ULCC.

Since three pairs of DL CCs and UL CCs are defined, UE can be said to beserved from three serving cells.

UE can monitor PDCCHs in a plurality of DL CCs and receive DL transportblocks through the plurality of DL CCs at the same time. UE can send aplurality of UL transport blocks through a plurality of UL CCs at thesame time.

A pair of a DL CC #A and an UL CC #A can become a first serving cell, apair of a DL CC #B and an UL CC #B can become a second serving cell, anda DL CC #C and an UL CC#C can become a third serving cell. Each servingcell can be identified by a Cell Index (CI). A CI can be unique within acell or can be UE-specific.

The serving cell can be divided into a primary cell and a secondarycell. The primary cell is a cell on which UE performs an initialconnection establishment procedure or initiates a connectionre-establishment procedure or a cell designated as a primary cell in ahandover process. The primary cell is also called a reference cell. Thesecondary cell can be configured after an RRC connection has beenestablished and can be used to provide additional radio resources. Atleast one primary cell is always configured, and a secondary cell can beadded/modified/released in response to higher layer signaling (e.g., anRRC message). The CI of a primary cell can be fixed. For example, thelowest CI can be designated as the CI of a primary cell.

The primary cell includes a downlink Primary Component Carrier (DL PCC)and an uplink PCC (UL PCC) in view of a CC. The secondary cell includesonly a downlink Secondary Component Carrier (DL SCC) or a pair of a DLSCC and an UL SCC in view of a CC.

ACK/NACK transmission for HARQ in 3GPP LTE Time Division Duplex (TDD) isdescribed below.

In TDD, unlike in a Frequency Division Duplex (FDD), a DL subframe andan UL subframe coexist in one radio frame. In general, the number of ULsubframes is smaller than that of DL subframes. Accordingly, inpreparation for a case where UL subframes for sending an ACK/NACK signalare not sufficient, a plurality of ACK/NACK signals for DL transportblocks received in a plurality of DL subframes is transmitted in one ULsubframe.

In accordance with section 10.1 of 3GPP TS 36.213 V8.7.0 (2009 May), twoACK/NACK modes: ACK/NACK bundling and ACK/NACK multiplexing areinitiated.

In ACK/NACK bundling, UE sends ACK if it has successfully decoded allreceived PDSCHs (i.e., DL transport blocks) and sends NACK in othercases. To this end, ACK or NACKs for each PDSCH are compressed throughlogical AND operations.

ACK/NACK multiplexing is also called ACK/NACK channel selection (orsimply channel selection). In accordance with ACK/NACK multiplexing, UEselects one of a plurality of PUCCH resources and sends ACK/NACK.

Table below shows DL subframes n−k associated with an UL subframe naccording to an UL-DL configuration in 3GPP LTE, wherein kεK and M isthe number of elements of a set K.

TABLE 5 UL-DL Config- Subframe n uration 0 1 2 3 4 5 6 7 8 9 0 — — 6 — 4— — 6 — 4 1 — — 7, 6 4 — — — 7, 6 4 — 2 — — 8, 7, — — — — 8, 7, — — 4, 64, 6 3 — — 7, 6, 11 6, 5 5, 4 — — — — — 4 — — 12, 8, 6, 5, — — — — — —7, 11 4, 7 5 — — 13, 12, 9, — — — — — — — 8, 7, 5, 4, 11, 6 6 — — 7 7 5— — 7 7 —

It is assumed that M DL subframes are associated with the UL subframe nand, for example, M=3. In this case, UE can obtain 3 PUCCH resourcesn⁽¹⁾ _(PUCCH,0), n⁽¹⁾ _(PUCCH,1), and n⁽¹⁾ _(PUCCH,2) because it canreceive 3 PDCCHs from 3 DL subframes. In this case, an example ofACK/NACK channel selection is the same as the following table.

TABLE 6 HARQ-ACK(0), HARQ-ACK(1), HARQ-ACK(2) n⁽¹⁾ _(PUCCH) b(0), b(1)ACK, ACK, ACK n⁽¹⁾ _(PUCCH,2) 1, 1 ACK, ACK, NACK/DTX n⁽¹⁾ _(PUCCH,1) 1,1 ACK, NACK/DTX, ACK n⁽¹⁾ _(PUCCH,0) 1, 1 ACK, NACK/DTX, NACK/DTX n⁽¹⁾_(PUCCH,0) 0, 1 NACK/DTX, ACK, ACK n⁽¹⁾ _(PUCCH,2) 1, 0 NACK/DTX, ACK,NACK/DTX n⁽¹⁾ _(PUCCH,1) 0, 0 NACK/DTX, NACK/DTX, ACK n⁽¹⁾ _(PUCCH,2) 0,0 DTX, DTX, NACK n⁽¹⁾ _(PUCCH,2) 0, 1 DTX, NACK, NACK/DTX n⁽¹⁾_(PUCCH,1) 1, 0 NACK, NACK/DTX, NACK/DTX n⁽¹⁾ _(PUCCH,0) 1, 0 DTX, DTX,DTX N/A N/A

In the above table, HARQ-ACK(i) indicates ACK/NACK for an i^(th) DLsubframe of M DL subframes. Discontinuous transmission (DTX) means thata DL transport block has not been received on a PDSCH in a correspondingDL subframe or that a corresponding PDCCH has not been detected. Inaccordance with Table 6, 3 PUCCH resources n⁽¹⁾ _(PUCCH,0), n⁽¹⁾_(PUCCH,1), and n⁽¹⁾ _(PUCCH,2) are present, and b(0), b(1) are two bitstransmitted using a selected PUCCH.

For example, when UE successfully receives all 3 DL transport blocks in3 DL subframes, the UE performs QPSK modulation on bits (1,1) using n⁽¹⁾_(PUCCH,2) and sends them on a PUCCH. If UE fails in decoding a DLtransport block in a first (i=0) DL subframe, but succeeds in decodingthe remaining transport blocks, the UE sends bits (1,0) on a PUCCH usingn⁽¹⁾ _(PUCCH,2). That is, in the existing PUCCH format 1b, only ACK/NACKof 2 bits can be transmitted. However, in channel selection, allocatedPUCCH resources are linked to an actual ACK/NACK signal in order toindicate more ACK/NACK states. This channel selection is also referredto as channel selection using the PUCCH format 1b.

In ACK/NACK channel selection, if at least one ACK is present, NACK andDTX are coupled. This is because all ACK/NACK states cannot berepresented by a combination of reserved PUCCH resources and a QPSKsymbol. If ACK is not present, however, DTX is decoupled from NACK.

The above-described ACK/NACK bundling and ACK/NACK multiplexing can beapplied in the case where one serving cell has been configured in UE inTDD.

For example, it is assumed that one serving cell has been configured(i.e., only a primary cell is configured) in UE in TDD, ACK/NACKbundling or ACK/NACK multiplexing is used, and M=1. That is, it isassumed that one DL subframe is associated with one UL subframe.

1) UE sends ACK/NACK in a subframe n if the UE detects a PDSCH indicatedby a corresponding PDCCH in a subframe n−k of a primary cell or detectsa Semi-Persistent Scheduling (SPS) release PDCCH. In LTE, a BS caninform UE that semi-persistent transmission and reception are performedin what subframes through a higher layer signal, such as Radio ResourceControl (RRC). Parameters given by the higher layer signal can be, forexample, the periodicity of a subframe and an offset value. When the UEreceives the activation or release signal of SPS transmission through aPDCCH after recognizing semi-persistent transmission through the RRCsignaling, the UE performs or releases SPS PDSCH reception or SPS PUSCHtransmission. That is, the UE does not immediately perform SPStransmission/reception although SPS scheduling is allocated theretothrough the RRC signaling, but when an activation or release signal isreceived through a PDCCH, performs SPS transmission/reception in asubframe that corresponds to frequency resources (resource block)according to the allocation of the resource block designated by thePDCCH, modulation according to MCS information, a subframe periodicityallocated through the RRC signaling according to a code rate, and anoffset value. Here, a PDCCH that releases SPS is called an SPS releasePDCCH, and a DL SPS release PDCCH that releases DL SPS transmissionrequires the transmission of an ACK/NACK signal.

Here, in the subframe n, UE sends ACK/NACK using the PUCCH formats 1a/1baccording to a PUCCH resource n^((1,p)) _(PUCCH). In n^((1,p)) _(PUCCH),p indicates an antenna port p. The k is determined by Table 5.

The PUCCH resource n^((1,p)) _(PUCCH) can be allocated as in thefollowing equation. P can be p0 or p1.n ^((1,p=p0)) _(PUCCH)=(M−m−1)·N _(c) +m·N _(c+1) n _(CCE) +N ⁽¹⁾_(PUCCH) for antenna port p=p0,n ^((1,p=p1)) _(PUCCH)=(M−m−1)·N _(c) +m·N _(c+1)+(n _(CCE)+1)+N ⁽¹⁾_(PUCCH) for antenna port p=p1,  [Equation 3]

In Equation 3, c is selected in such a way as to satisfyN_(c)≦n_(CCE)<N_(c+1)(antenna port p0),N_(c)≦(n_(CCE)+1)<N_(c+1)(antenna port p1) from among {0, 1, 2, 3}. N⁽¹⁾_(PUCCH) is a value set by a higher layer signal. N_(C)=max{0, floor[N^(DL) _(RB)·(N^(RB) _(sc)·c−4)/36]}. The N^(DL) _(RB) is a DLbandwidth, and N^(RB) _(sc) is the size of an RB indicated by the numberof subcarriers in the frequency domain. n_(CCE) is a first CCE numberused to send a corresponding PDCCH in a subframe n−km. m is a value thatmakes km the smallest value in the set K of Table 5.

2) If UE detects an SPS PDSCH, that is, a PDSCH not including acorresponding PDCCH, in the DL subframe n−k of a primary cell, the UEcan send ACK/NACK in the subframe n using the PUCCH resource n^((1,p))_(PUCCH) as follows.

Since an SPS PDSCH does not include a scheduling PDCCH, UE sendsACK/NACK through the PUCCH formats 1a/1b according to n^((1,p)) _(PUCCH)that is configured by a higher layer signal. For example, 4 resources (afirst PUCCH resource, a second PUCCH resource, a third PUCCH resource,and a fourth PUCCH resource) can be reserved through an RRC signal, andone resource can be indicated through the Transmission Power Control(TPC) field of a PDCCH that activates SPS scheduling.

The following table is an example in which resources for channelselection are indicated by a TPC field value.

TABLE 7 TPC field value Resource for channel selection ‘00’ First PUCCHresource ‘01’ Second PUCCH resource ‘10’ Third PUCCH resource ‘11’Fourth PUCCH resource

For another example, it is assumed that in TDD, one serving cell isconfigured (i.e., only a primary cell is configured) in UE, ACK/NACKmultiplexing is used, and M>1. That is, it is assumed that a pluralityof DL subframes is associated with one UL subframe.

1) A PUCCH resource n⁽¹⁾ _(PUCCH,i) for sending ACK/NACK when UEreceives a PDSCH in a subframe n−k_(i) (0≦i≦M−1) or detects a DL SPSrelease PDCCH can be allocated as in the following equation. Here,k_(i)εK, and the set K has been described with reference to Table 5.n ⁽¹⁾ _(PUCCH,i)=(M−i−1)·N _(c) +i·N _(c+1) +n _(CCE,i) +N ⁽¹⁾_(PUCCH)  [Equation 4]

Here, c is selected from {0, 1, 2, 3} so that N_(c)≦n_(CCE,i)<N_(c+1) issatisfied. N⁽¹⁾ _(PUCCH) is a value set by a higher layer signal.N_(C)=max{0, floor [N^(DL) _(RB)·(N^(RB) _(sc)·c−4)/36]}. The N^(DL)_(RB) is a DL bandwidth, and N^(RB) _(sc) is the size of an RB indicatedby the number of subcarriers in the frequency domain. n_(CCE,i) is afirst CCE number used to send a corresponding PDCCH in the subframen−k_(i).

2) If UE receives a PDSCH (i.e., SPS PDSCH) not having a correspondingPDCCH in the subframe, n⁽¹⁾ _(PUCCH,i) is determined by a configurationgiven by a higher layer signal and Table 7.

If two or more serving cells have been configured in UE in TDD, the UEsends ACK/NACK using channel selection that uses the PUCCH format 1b orthe PUCCH format 3. Channel selection that uses the PUCCH format 1b usedin TDD can be performed as follows.

If a plurality of serving cells using channel selection that uses thePUCCH format 1b has been configured, when ACK/NACK bits are greater than4 bits, UE performs spatial ACK/NACK bundling on a plurality ofcodewords within one DL subframe and sends spatially bundled ACK/NACKbits for each serving cell through channel selection that uses the PUCCHformat 1b. Spatial ACK/NACK bundling means the compression of ACK/NACKfor each codeword through logical AND operations within the same DLsubframe.

If ACK/NACK bits are 4 bits or lower, spatial ACK/NACK bundling is notused and the ACK/NACK bits are transmitted through channel selectionthat uses the PUCCH format 1b.

If 2 or more serving cells using the PUCCH format 3 have been configuredin UE, when ACK/NACK bits are greater than 20 bits, spatial ACK/NACKbundling can be performed in each serving cell and ACK/NACK bitssubjected to spatial ACK/NACK bundling can be transmitted through thePUCCH format 3. If ACK/NACK bits are 20 bits or lower, spatial ACK/NACKbundling is not used and the ACK/NACK bits are transmitted through thePUCCH format 3.

<Channel Selection Using the PUCCH Format 1b Used in FDD>

If two serving cells using FDD have been configured in UE, ACK/NACK canbe transmitted through channel selection that uses the PUCCH format 1b.The UE can feed ACK/NACK for a maximum of 2 transport blocks, receivedin one serving cell, back to a BS by sending 2-bit (b(0)b(1))information in one PUCCH resource selected from a plurality of PUCCHresources. One codeword can be transmitted in one transport block. APUCCH resource can be indicated by a resource index n⁽¹⁾ _(PUCCH,i).Here, A is any one of {2, 3, 4}, and i is 0≦i≦(A−1). The 2-bitinformation is indicated as b(0)b(1).

HARQ-ACK(j) indicates an HARQ ACK/NACK response that is related to atransport block or DL SPS release PDCCH transmitted by a serving cell.The HARQ-ACK(j), the serving cell, and the transport block can have thefollowing mapping relationship.

TABLE 8 HARQ-ACK(j) A HARQ-ACK(0) HARQ-ACK(1) HARQ-ACK(2) HARQ-ACK(3) 2Transport block 1 Transport block 2 of NA NA of primary cell secondarycell 3 Transport block 1 Transport block 2 of Transport block 3 of NA ofserving cell 1 serving cell 1 serving cell 2 4 Transport block 1Transport block 2 of Transport block 3 of Transport block 4 of ofprimary cell primary cell secondary cell secondary cell

In Table 8, for example, in the case of A=4, HARQ-ACK(0) and HARQ-ACK(1)indicate ACK/NACKs for 2 transport blocks transmitted in a primary cell,and HARQ-ACK(2) and HARQ-ACK(3) indicate ACK/NACKs for 2 transportblocks transmitted in a secondary cell.

When UE receives a PDSCH or detects a DL SPS release PDCCH by detectinga PDCCH in a subframe ‘n−4’ of a primary cell, the UE sends ACK/NACKusing a PUCCH resource n⁽¹⁾ _(PUCCH,i). Here, n⁽¹⁾ _(PUCCH,i) isdetermined to be n_(CCE,i)+N⁽¹⁾ _(PUCCH). Here, n_(CCE,i) means an indexof the first CCE that is used to send a PDCCH by a BS, and N⁽¹⁾ _(PUCCH)is a value set through a higher layer signal. If a transmission mode ofa primary cell supports up to two transport blocks, a PUCCH resourcen⁽¹⁾ _(PUCCH,i+1) is given. Here, n⁽¹⁾ _(PUCCH,i+1) can be determined tobe n_(CCE,i)+1+N⁽¹⁾ _(PUCCH). That is, if a primary cell is set in atransmission mode in which a maximum of up to 2 transport blocks can betransmitted, 2 PUCCH resources can be determined.

If a PDCCH detected in a subframe ‘n−4’ of a primary cell is notpresent, a PUCCH resources n⁽¹⁾ _(PUCCH,i) for sending ACK/NACK for aPDSCH is determined by a higher layer configuration. If up to 2transport blocks are supported, a PUCCH resource n⁽¹⁾ _(PUCCH,i+1) canbe given as n⁽¹⁾ _(PUCCH,i+1)=n⁽¹⁾ _(PUCCH,i+1).

If a PDSCH is received in a secondary cell by detecting a PDCCH in asubframe ‘n−4’, PUCCH resources n⁽¹⁾ _(PUCCH,i) and n⁽¹⁾ _(PUCCH,i+1)for a transmission mode in which up to 2 transport blocks are supportedcan be determined by a higher layer configuration.

In the prior art, it was a precondition that a plurality of servingcells configured in UE uses radio frames having the same type. Forexample, it was a precondition that all of a plurality of serving cellsconfigured in UE use FDD frames or use TDD frames. In thenext-generation wireless communication system, however, different typesof radio frames may be used in serving cells.

FIG. 10 shows one example in which a plurality of serving cells usesdifferent types of radio frames in a wireless communication system.

Referring to FIG. 10, a primary cell PCell and a plurality of secondarycells SCell #1, . . . , SCell #N can be configured in UE. In this case,the primary cell can operate in FDD and use an FDD frame, and thesecondary cells can operate in TDD and use TDD frames. The same UL-DLconfiguration can be used in the plurality of secondary cells. A DLsubframe (indicated by D) and an UL subframe (indicated by U) arepresent in a 1:1 relationship in the primary cell, but a DL subframe andan UL subframe may be present in ratios not 1:1 in the secondary cells.

Table 9 below shows that ACK/NACK is transmitted in what a subframeaccording to an UL-DL configuration when one serving cell operates inTDD.

TABLE 9 UL-DL Config- Subframe n uration 0 1 2 3 4 5 6 7 8 9 0 4 6 — 4 6— 1 7 6 4 7 6 4 2 7 6 4 8 7 6 4 8 3 4 11  7 6 6 5 5 4 12  11  8 7 7 6 54 5 12  11  9 8 7 6 5 4 13  6 7 7 7 7 5

In Table 9, when UE receives a PDSCH or a PDCCH (e.g., DL SPS releasePDCCH) necessary for an ACK/NACK response in a subframe n, the UE sendsACK/NACK in a subframe ‘n+k(n)’. Each of the values of Table 9 indicatesthe k(n) value. For example, Table 9 indicates that if an UL-DLconfiguration is 0 and a PDSCH is received in a subframe 0, ACK/NACK istransmitted in a subframe 4 after four subframes. A specific time isnecessary in order for UE to send ACK/NACK after receiving a PDSCH or aDL SPS release PDCCH. A minimum value of this specific time ishereinafter indicated as ‘k_(min)’, and a value of ‘k_(min)’ can be foursubframes. In Table 9, a point of time at which ACK/NACK is transmittedis described below. It can be seen that ACK/NACK is chiefly transmittedin the first UL subframe after elapses. However, an underline number inTable 9 does not indicates the first UL subframe after ‘k_(min)’elapses, but indicates an UL subframe placed next. This is forpreventing ACK/NACK for too many DL subframes from being transmitted inone UL subframe. It is difficult to apply this ACK/NACK transmissiontiming in TDD to a wireless communication system that uses differenttypes of radio frames without change.

In a wireless communication system, UL control information, such asACK/NACK, can be transmitted through a specific serving cell, that is, aprimary cell. In the prior art, it was a precondition that all servingcells use radio frames having the same type. ACK/NACK transmissiontiming, that is, HARQ timing, was determined based on this assumption.If a plurality of serving cells uses different types of radio frames, itis necessary to define that ACK/NACK will be transmitted using whatmethod.

It is hereinafter assumed that a primary cell and at least one secondarycell are configured in UE in a wireless communication system. It is alsoassumed that the primary cell uses an FDD frame and the secondary celluses a TDD frame. Any one of the UL-DL configurations of Table 1 can beused in the TDD frame. Hereinafter, only a relationship between aprimary cell and one secondary cell is illustrated, for convenience ofdescription, but this relationship can be applied to a relationshipbetween a primary cell and each of a plurality of secondary cells whenthe plurality of secondary cells is configured in UE.

Under this assumption, first, a method of transmitting ACK/NACK fordownlink data received through a primary cell is described below.Hereinafter, the downlink data generally indicates a PDSCH that requestsan ACK/NACK response, a codeword included in a PDSCH, a DL SPS releasePDCCH indicating a DL SPS release and the like.

FIG. 11 shows a method of transmitting ACK/NACK for downlink datareceived through a primary cell.

Referring to FIG. 11, a BS sends downlink data in the subframe n of aprimary cell (S110). UE receives the downlink data in the subframe n ofthe DL PCC of the primary cell.

The UE decodes the downlink data and generates ACK/NACK for the downlinkdata (S120).

The UE sends the ACK/NACK in the subframe n+k_(PCC)(n) of the primarycell (S130).

The subframe n+k_(PCC)(n) of the primary cell is a subframe after aminimum delay time (this is called k_(min)) necessary for an ACK/NACKresponse has elapsed from a point of time at which the downlink data wasreceived. Here, the minimum delay time k_(min) may be four subframes.Accordingly, the UE can send the ACK/NACK in the subframe n+4 of the ULPCC of the primary cell.

That is, in the primary cell, as in the case where an HARQ is performedin conventional FDD, the ACK/NACK is transmitted in a subframe afterfour subframes elapse from a subframe in which data was received.

A method of UE sending ACK/NACK when the UE receives downlink data in asecondary cell is described below.

FIG. 12 shows a method of transmitting ACK/NACK for downlink datareceived through a secondary cell.

Referring to FIG. 12, a BS sends information about the UL-DLconfiguration of a secondary cell (S210). The secondary cell may needthe UL-DL configuration information because it operates in TDD. TheUL-DL configuration information can be transmitted through a higherlayer signal, such as an RRC message.

A BS sends downlink data in the subframe n of the secondary cell (S220).

The UE decodes the downlink data and generates ACK/NACK for the downlinkdata (S230).

The UE can send the ACK/NACK to the BS through the subframe n+k_(SCC)(n)of a primary cell (S240). The subframe n+k_(SCC)(n) can be determined bythe following method.

<Method 1>

Method 1 is a method in which the subframe n+k_(SCC)(n) complies withACK/NACK transmission timing in the primary cell. That is, Method 1 is amethod of configuring the UL subframe of the primary cell that is thesame as n+k_(min) as the subframe n+k_(SCC)(n). In other words, if datais received in the subframe n of a secondary cell, ACK/NACK for the datais transmitted in the subframe n+k_(min) of a primary cell. Here,k_(min) can be, for example, four subframes.

FIG. 13 shows Method 1 when ‘k_(min)’ is four subframes.

Referring to FIG. 13, downlink data is received in the DL subframe of asecondary cell using a TDD frame, and ACK/NACK for the downlink data istransmitted in the UL subframe of a primary cell. It can be seen thatthe UL subframe is a subframe placed after four subframes from the DLsubframe of the secondary cell.

In accordance with Method 1, there is an advantage in that ACK/NACKdelay is minimized because ACK/NACK for downlink data received in asecondary cell is always transmitted after k_(min) subframes on thebasis of a point of time at which the downlink data was received.

Furthermore, in conventional TDD, if the number of DL subframescorresponding to one UL subframe is many, there is a problem in that thenumber of ACK/NACKs that must be transmitted in the one UL subframe isincreased. However, Method 1 is advantageous in that ACK/NACKtransmission is distributed.

If the UL subframe of a primary cell in which ACK/NACK is transmitted isa subframe n, the number of ACK/NACK resources that need to be securedin the subframe n can be determined by a transmission mode of theprimary cell for a subframe n−k_(min) and a transmission mode in the DLsubframe of a secondary cell.

In accordance with Method 1, ACK/NACK timing applied to UE may berepresented by changing Table 5 into Table 10 below.

TABLE 10 UL-DL Config- Subframe n uration 0 1 2 3 4 5 6 7 8 9 0 4 — — —4 4 — — — 4 1 4 — — 4 4 4 — — 4 4 2 4 — 4 4 4 4 — 4 4 4 3 4 4 4 4 4 4 —— — 4 4 4 4 4 4 4 4 — — 4 4 5 4 4 4 4 4 4 — 4 4 4 6 4 — 4 4 4 — 4

That is, if the UL-DL configuration of a secondary cell is the same asany one of Table 10 and a primary cell uses an FDD frame, a subframe nis a subframe in which ACK/NACK is transmitted and a number indicated inthe subframe n indicates k_(min). Here, the subframe n−k_(min) indicatesa subframe in which downlink data, that is, the subject of ACK/NACK, isreceived. For example, in Table 10, an UL-DL configuration is 0, and 4is written in a subframe 9. In this case, it indicates that ACK/NACK fordownlink data received in the subframe 5 (=9−4) of a secondary cell istransmitted in the subframe 9.

In accordance with Method 1, ACK/NACK timing applied to UE may berepresented by changing Table 9 into Table 11 below.

TABLE 11 UL-DL Config- Subframe n uration 0 1 2 3 4 5 6 7 8 9 0 4 4 — 44 — 1 4 4 4 4 4 4 2 4 4 4 4 4 4 4 4 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 54 4 4 4 4 4 4 4 4 6 4 4 4 4 4

In Table 11, a subframe n indicates a subframe in which downlink data isreceived. A subframe n+k_(SCC)(n) is a subframe in which ACK/NACK forthe downlink data is transmitted. Each of values in Table 11 indicate ak_(SCC)(n) value for the subframe n. For example, it indicates that ifan UL-DL configuration is 0 and downlink data is received in thesubframe 1 of a secondary cell, ACK/NACK is transmitted in a subframe 5(of a primary cell) after four subframes.

Tables 10 and 11 and FIG. 13 have a precondition that the radio frameboundaries of a secondary cell and a primary cell are the same. That is,it is a precondition that the radio frame of the primary cell issynchronized with the radio frame of the secondary cell. If the radioframe of the primary cell is not synchronized with the radio frame ofthe secondary cell, additional subframe delay (indicated by k_(add)) forcompensating for this asynchronization can be taken into consideration.That is, in Method 1, k_(SCC)(n) may be changed into k_(min)+k_(add).

Or, assuming that downlink data is received in the subframe n of asecondary cell and a subframe in which ACK/NACK for the downlink data istransmitted is n+k_(SCC)(n), if the k_(SCC)(n) is smaller thank_(min)+k_(add), scheduling may be limited so that the downlink data isnot transmitted in the subframe n of the secondary cell.

<Method 2>

Method 2 is a method of determining a subframe n+k_(SCC)(n) in whichACK/NACK is transmitted based on TDD ACK/NACK transmission timing in asecondary cell. That is, k_(SCC)(n) is determined as in Table 9, butactual ACK/NACK is transmitted through the UL PCC of a primary cell.

FIG. 14 shows Method 2.

Referring to FIG. 14, downlink data is received in the DL subframe of asecondary cell using a TDD frame, and ACK/NACK for the downlink data istransmitted in the UL subframe of a primary cell. Here, timing at whichthe ACK/NACK is transmitted complies with TDD ACK/NACK transmissiontiming in the secondary cell. That is, k_(SCC)(n) can be determined asin Table 9.

Or, if ACK/NACK for downlink data received in a subframe n−k_(i) isdefined to be transmitted in a subframe n, Table 5 may be used todetermine the ki value. Referring to Table 5, for example, if the UL-DLconfiguration of a secondary cell is 0, ACK/NACK transmitted in thesubframe 2 is for downlink data received in a subframe prior to 6subframes. Or, if the UL-DL configuration is 2, ACK/ANCK transmitted inthe subframe 2 is for downlink data received prior to 8, 7, 4 or 6subframes. In this case, however, ACK/NACK transmission is performedthrough the UL PCC of a primary cell not the secondary cell.

Method 2 is advantageous in that ACK/NACK timing when one serving celloperating in TDD is configured in UE and the serving cell is used as aprimary cell can be applied to a case where a serving cell is used as asecondary cell without change.

Assuming that the subframe of a primary cell in which ACK/NACK istransmitted is a subframe n, the number of ACK/NACK resources to besecured in the subframe n is determined by the number of DL subframes ofa corresponding primary cell and secondary cell, a transmission mode inthe DL subframe of the secondary cell and the like.

If the radio frame of a primary cell is not synchronized with that of asecondary cell, additional subframe delay (indicated by k_(add)) forcompensating for this asynchronization can be taken into consideration.The k_(add) may be a fixed value or may be a value set through an RRCmessage. In Method 2, assuming that k′_(SCC)(n)=k_(SCC)(n)+k_(add),ACK/NACK for downlink data received in the subframe n of a secondarycell may be represented as being transmitting in the UL subframen+k′_(SCC)(n) of a primary cell.

Or, assuming that downlink data is received in the subframe n of asecondary cell and a subframe in which ACK/NACK for the downlink data istransmitted is n+k_(SCC)(n), if the k_(SCC)(n) is smaller thank_(min)+k_(add), scheduling may be limited so that the downlink data isnot transmitted in the subframe n of the secondary cell.

If Method 1 is used as the method of transmitting ACK/NACK in a primarycell and the method of transmitting ACK/NACK for a secondary cell,ACK/NACK for a primary cell and a secondary cell can comply with anACK/NACK transmission scheme used in FDD. For example, channel selectionthat uses the PUCCH format 1b used in FDD when a plurality of servingcells is configured in UE can be used. That is, ACK/NACK for thesecondary cell is transmitted using channel selection that uses thePUCCH format 1b through a primary cell without using a compressionscheme, such as ACK/NACK bundling. A compression scheme, such asACK/NACK bundling, may be used because only one DL subframe isassociated with one UL subframe of a primary cell.

In contrast, if Method 2 is used as the method of transmitting ACK/NACKin a primary cell and the method of transmitting ACK/NACK for asecondary cell, ACK/NACK for a primary cell and a secondary cell cancomply with an ACK/NACK transmission scheme used in TDD. For example,ACK/NACK can be transmitted through channel selection that uses thePUCCH format 1b used when a plurality of serving cells is configured inTDD.

In an aggregation of serving cells to which different types of radioframes are applied, if UL transmission and DL reception are present inthe same time interval, interference attributable to the UL transmissioncan occur in the DL reception. Accordingly, UL transmission and DLreception are not preferred in neighboring frequency bands. To this end,frequency bands can be grouped according to frequency bands that arespaced apart from one another without making interference with them, anddifferent types of radio frames can be used according to the spacedfrequency band group. UE that uses each frequency band group can have anindependent wireless frequency transmission module and use an additionalpower amplifier.

Furthermore, unlike in the prior art in which a control signal-dedicatedchannel on which ACK/NACK is carried is transmitted through only aprimary cell, a PUCCH can be transmitted in a specific serving cell thatbelongs to a frequency band group other than frequency band groups towhich a primary cell belongs. In this case, ACK/NACK timing (i.e., HARQtiming) transmitted in the PUCCH is not problematic even in existingACK/NACK timing.

A DCI format used in a carrier aggregation system in which differenttypes of radio frames are used is described below.

In the case of an existing TDD system, since a plurality of DL subframesis associated with one UL subframe, a Downlink Assignment Index (DAI)field of 2 bits is included in a PDCCH on which a downlink grant iscarried or a PDCCH on which an uplink grant is carried and thentransmitted in order to prevent an ACK/NACK error in the UL subframe.

The DAI included in the PDCCH on which the downlink grant is carriedincludes information about order of PDSCHs that are transmitted in theDL subframes corresponding to the UL subframe. The DAI included in thePDCCH on which the uplink grant is carried includes information aboutthe sum of the number of DL subframes corresponding to the UL subframeand the number of DL SPS release PDCCHs.

Meanwhile, if serving cells operating in TDD are aggregated, a DAIincluded in a PDCCH on which an uplink grant is carried becomesinformation capable of determining the size of an ACK/NACK payload thatis piggybacked to a PUSCH. For example, information about a maximumvalue can be obtained from the sum of a total number of PDSCHs that aretransmitted in DL subframes associated with one UL subframe and thenumber of DL SPS release PDCCHs on the basis of each of serving cellsaggregated through a DAI that is included in a PDCCH on which an uplinkgrant is carried. The size of a piggybacked ACK/NACK payload can bedetermined using the maximum value. If serving cells operating in FDDare aggregated, a DAI is not necessary because a DL subframe correspondsto an UL subframe in a 1:1 manner.

In the present invention, a serving cell operating in FDD and a servingcell operating in TDD are aggregated. Accordingly, in this case, how aDAI field will be configured is problematic.

1. Adding a DAI Field to the DCI of a Serving Cell Operating in FDD.

A DAI field can be added to a DCI that is transmitted in a serving celloperating in FDD. Accordingly, when a serving cell operating in FDD anda serving cell operating in TDD have a constant frequency band, the sameDCI formats on which the two serving cells are scheduled can be made tohave the same size. In this case, UE can use the same searching spacewhen searching for a PDCCH although the UE uses different types of radioframes in the serving cells. If the DCI formats do not have the samesize although a DAI field is added (e.g., the DCI formats may not havethe same size because frequency bands between the two serving cellsdiffer), the DCI formats can be made to have the same size by addingpadding bits.

Or, a DAI field can be added to some of DCIs transmitted in servingcells that operate in FDD. For example, a DAI field can be added to onlythe DCI formats 0/1A.

The DAI field added as described above can be used for other purposesnot for the original use. For example, a DAI field is not basicallypresent in a PDCCH on which an uplink grant for scheduling a primarycell operating in FDD is carried, but if a DAI is included in the PDCCH,the PDCCH can carry information necessary when ACK/NACK is piggybackedto a PUSCH as in TDD. This method can be applied to Method 2.

2. Removing a DAI Field in the DCI of a Serving Cell Operating in TDD.

A DAI field is basically present in a DCI transmitted in a serving celloperating in TDD, but this DAI field can be removed. In this case, whena serving cell operating in FDD and a serving cell operating in TDD havea constant frequency band size, the same DCI formats on which the twoserving cells are scheduled can be made to have the same size. In thiscase, UE can use the same searching space when searching for a PDCCHalthough the UE uses different types of radio frames in the servingcells. If the DCI formats do not have the same size although the DAIfield is added (e.g., for a reason, such as that the frequency bands ofthe two serving cells do not have the same size), the DCI formats can bemade to have the same size by adding padding bits to a DCI format havinga smaller size. This method can be applied to Method 1.

As described in the 1 and 2, assuming that a downlink grant forperforming scheduling on the downlink data of a primary cell is called afirst downlink grant and a downlink grant for performing scheduling onthe downlink data of a secondary cell is called a second downlink grant,the number of bits of the first downlink grant can be configured to bethe same as that of the second downlink grant.

FIG. 15 is a block diagram showing a wireless device in which anembodiment of the present invention is implemented.

A BS 100 includes a processor 110, memory 120, and a Radio Frequency(RF) unit 130. The processor 110 implements the proposed functions,processes and/or methods. For example, the processor 110 sendsinformation about the UL-DL configuration of a secondary cell and sendsdata to UE through a primary cell or a secondary cell. Furthermore, theprocessor 110 receives ACK/NACK for the data in a subframe configured ina primary cell. This method has been described with reference to FIGS.10 to 14. The memory 120 is connected to the processor 110, and itstores various pieces of information for driving the processor 110. TheRF unit 130 is connected to the processor 110, and it sends and/orreceives radio signals.

UE 200 includes a processor 210, memory 220, and an RF unit 230. Theprocessor 210 implements the proposed functions, processes and/ormethods. For example, the processor 210 receives information about theUL-DL configuration of a secondary cell from a BS and receives datathrough a primary cell or a secondary cell. Thereafter, the processor210 sends ACK/NACK for the data in accordance with the methods describedwith reference to FIGS. 10 to 14 in a primary cell. The memory 220 isconnected to the processor 210, and it stores various pieces ofinformation for driving the processor 210. The RF unit 230 is connectedto the processor 210, and it sends and/or receives radio signals.

The processor 110, 210 may include Application-Specific IntegratedCircuits (ASICs), other chipsets, logic circuits, data processingdevices and/or converters for mutually converting baseband signals andradio signals. The memory 120, 220 may include Read-Only Memory (ROM),Random Access Memory (RAM), flash memory, memory cards, storage mediaand/or other storage devices. The RF unit 130, 230 may include one ormore antennas for transmitting and/or receiving radio signals. When anembodiment is implemented in software, the above-described scheme may beimplemented as a module (process, function, etc.) for performing theabove-described function. The module may be stored in the memory 120,220 and executed by the processor 110, 210. The memory 120, 220 may beplaced inside or outside the processor 110, 210 and connected to theprocessor 110, 210 using a variety of well-known means.

Although the some embodiments of the present invention have beendescribed above, a person having ordinary skill in the art willappreciate that the present invention may be modified and changed invarious ways without departing from the technical spirit and scope ofthe present invention. Accordingly, the present invention is not limitedto the embodiments and it may be said that the present inventionincludes all embodiments within the scope of the claims below.

What is claimed is:
 1. A method for transmitting anacknowledgement/not-acknowledgement (ACK/NACK) by User Equipment (UE)for which a plurality of serving cells have been configured, the methodcomprising: receiving data in a subframe n of a secondary cell; andtransmitting an ACK/NACK signal for the data in a subframe n+k of aprimary cell, wherein the primary cell uses a Frequency Division Duplex(FDD) radio frame, wherein the secondary cell uses a Time DivisionDuplex (TDD) radio frame, wherein k is a predetermined value, whereinuplink (UL)-downlink (DL) configuration information about the TDD radioframe used in the secondary cell is received by the UE, and wherein theUL-DL configuration information indicates any one of the UL-DLconfigurations shown in the table below: Uplink- Downlink- downlinkto-Uplink config- Switch-point Subframe number n uration periodicity 0 12 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 25 ms D S U D D D S U D D 3 10 ms D S U U U D D D D D 4 10 ms D S U U D DD D D D 5 10 ms D S U D D D D D D D 6 5 ms D S U U U D S U U  D.


2. The method of claim 1, wherein k is equal to the ACK/NACK timing inthe primary cell, and wherein ACK/NACK timing is a number of subframesafter receiving data.
 3. The method of claim 1, further comprising:receiving data in a subframe n of the primary cell; and transmitting anACK/NACK signal in the subframe n+k of the primary cell.
 4. The methodof claim 3, further comprising: receiving a first downlink grant, in theprimary cell, for the data received in the subframe n of the primarycell; and receiving a second downlink grant, in the primary cell, forthe data received in the subframe n of the secondary cell, wherein anumber of bits of the first downlink grant is equal to a number of bitsof the second downlink grant.
 5. The method of claim 1, wherein theuplink (UL)-downlink (DL) configuration information about the TDD radioframe used in the secondary cell is received through the primary cell.6. The method of claim 1, further comprising: receiving data in asubframe n of a third cell; and transmitting an ACK/NACK signal fordata, received in the third cell, in the subframe n+k of the primarycell which is associated with the subframe n of the third cell, whereinthe third cell is another secondary cell additionally allocated to theUE in addition to the primary cell and the secondary cell, and whereinthe third cell uses a TDD radio frame.
 7. User Equipment (UE),comprising: a Radio Frequency (RF) unit transmitting and receiving radiosignals; and a processor connected to the RF unit, wherein the processorreceives data in a subframe n of a secondary cell and transmits anacknowledgement/not-acknowledgement (ACK/NACK) signal for the data in asubframe n+k of a primary cell, wherein the primary cell uses aFrequency Division Duplex (FDD) radio frame, wherein the secondary celluses a Time Division Duplex (TDD) radio frame, wherein k is apredetermined value, wherein uplink (UL)-downlink (DL) configurationinformation about the TDD radio frame used in the secondary cell isreceived, and wherein the UL-DL configuration information indicates anyone of the UL-DL configurations shown in the table below: Uplink-Downlink- downlink to-Uplink config- Switch-point Subframe number nuration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms D S U U U D DD D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D D D D D 6 5 ms D SU U U D S U U  D.


8. The UE of claim 7, wherein k is a value equal to ACK/NACK timing inthe primary cell, and wherein ACK/NACK timing is a number of subframesafter receiving data.
 9. The method of claim 1, wherein the k is equalto
 4. 10. The UE of claim 7, wherein the k is equal to 4.